Stabilizing developed silver halide emulsions with heterocyclic thiol compounds

ABSTRACT

BY PROCESSING A SILVER HALIDE PHOTOGRAPHIC EMULSION LAYER HAVING DEVELOPED IMAGES IN A STABILIZING SOLUTION CONTAINING A SILVER COMPLEX FORMING AGENT OR A SUBSEQUENT AFTER-TREATING SOLUTION, WHICH CONTAINS A SPECIFIC THIOL COMPOUND, SUCH AS 2-MERCAPTOIMIDAZOLE,THE DECREASE IN ITS DENSITY AND THE DISCOLORATION DURING PRESERVATION, CAUSED BY THE SILVER COMPLEX FORMING AGENT REMAINING IN THE LAYER, CAN BE PREVENTED.

United States Patent Office 3,627,531 STABILIZING DEVELOPED SILVER HALIDE EMULSIONS WITH HETEROCYCLIC THIOL COMPGUNDS Fumihiko Nishio, Mitsunori Sugiyama, and Kintaro Nasu, KanagaWa-ken, Japan, assignors to Fuji Photo Film Co., Ltd., Kanagawa-ken, Japan No Drawing. Continuation-impart of application 557,352,

June 14, 1966, which is a continuation-in-part of application Ser. No. 218,167, Aug. 20, 1962. This application Aug. 19, 1968, Ser. No. 753,699

Claims priority, application Japan, Dec. 25, 1961, 36/47,119 Int. Cl. G03c 5/38 U.S. Cl. 96-61 2 Claims ABSTRACT OF THE DISCLOSURE By processing a silver halide photographic emulsion layer having developed images in a stabilizing solution containing a silver complex forming agent or a subsequent after-treating solution, which contains a specific thiol compound, such as Z-mercaptoimidazole, the decrease in its density and the discoloration during preservation, caused by the silver complex forming agent remaining in the layer, can be prevented.

This application is a continuation-in-part of our copending application U.S. Ser. No. 557,352, filed June 14, 1966, now abandoned, which is a continuation-in-part application of our U.S. application Ser. No. 218,167, filed Aug. 20, 1962, now abandoned.

This invention relates to a process for the production of photographic stable visible images in a photographic silver halide emulsion layer, and more particularly to a method for stabilizing the developed image without necessary fixing and washing.

Fixing and washing followed thereby are carried out in order to remove silver halide in the non-exposed parts after development. However, since the water soluble silverthiosulfate complex formed during fixing is unstable to light, it must be removed by washing with water.

Many silver complex forming agents which are effective as stabilizers have been reported in some technical literatures (for example: H. D. Russell, B. C. Yackel, and G. S. Bruce PSA Journal 16B 59-62 (1950)). However, there still exists no stabilizer fully satisfactory with respect to solubility, toxicity, smell, color of the formed silver complex, and stability to fading of the image. Generally known stabilizers are thiol compounds represented by the general formula RSH Where R is an aliphatic, aromatic or heterocyclic compound with a free SH group. Most thiol compounds are difiicultly soluble in an acidic solution and form yellow silver salts or complex salts. Further, they are usually toxic and have an offensive smell (ref. H. D. Russell: Photographic Engineering, 2(3), 136 (1951)). Thus due to defective properties, a thiol compound alone is of no practical use. Generally, alkali metal thiocyanates and ammonium thiocyanate are used as stabilizers.

The silver-thiocyanate complex is a transparent crystal and locates at white or transparent parts. Since this salt is stable to light it is unnecessary to remove it by washing with water (ref. British patent specification No. 867,242, French patent specifications No. 1,206,359, No. 1,239,429 and No. 1,258,356). Such treatment for stabilization enables rapid treatment but it is attended by many disadvantages in the quality of the image. In order to secure the stabilization to light, the silver complex forming agent is used in excess of the theoretical amount. Because of the hygroscopic property of the agent, the surface of the 3,627,531 Patented Dec. 14, 1971 processed emulsion layer tends to become sticky. The silver complex forming agent gradually oxidizes metallic silver constituting the image, converts it into a silver complex and decreases the density of the image or causes the image to disappear. In other words, if photosensitive materials after being subjected to the stabilizing treatment are placed in an atmospheric condition, the decrease in density, and the change in color from black to brown to yellow becomes remarkable with the lapse of time, and in an extreme case the image disappears. Such fading phenomenon is often observed when the material is preserved under high humidity. If the exposure is effected before the completion of reaction between unexposed silver halide and silver complex forming agent, the photolysis of unstable silver complex salt and unstabilized silver halide occurs and the white part or the transparent part is contaminated.

Alkali metal thiocyanates and ammonium thiocyanate have defects as aforementioned, but these thiocyanates exceed the other stabilizers in solubility, and are nonodorous and easily obtainable, and a colorless silver complex salt can be obtained using them.

It is, therefore, an object of the present invention to provide an improved method of stabilization using alkali metal thiocyanates or ammonium thiocyanate.

Another object is to prevent decrease in density, change in tone or contamination of the white part or transparent part of the image by light when the photographic image obtained by the stabilizing treatment is preserved in an atmospheric condition.

Still another object is to modify said stabilizers so that good properties are retained and the defects are removed.

These objects are accomplished by developing a latent image formed in a silver halide emulsion layer containing a developing agent in an alkaline solution either stabilizing the layer in an aqueous solution containing a silver complex forming agent, such as an alkali metal thiocyanate or ammonium thiocyanate, and at least 0.01%, based on the weight of the silver complex forming agent, of a thiol compound as below-mentioned, or stabilizing the layer in a first aqueous solution containing the silver complex forming agent, followed by processing the layer with a second aqueous solution containing at least 0.01%, based on the weight of the silver complex forming agent, of the thiol compound when compared on the basis of the same volume. That is, the concentration of the thiol compound in the second solution is at least 0.01% of the concentration of the silver complex forming agent in the first solution. The thiol compound used in the process of this invention is represented by the general formula:

wherein represents a member selected from the group consisting of imidazolyl, benzimidazolyl, thiazolyl, benzothiazolyl, oxazolyl, benzoxazolyl, thiadiazolyl, thiadiazolinyl, oxadiazolyl, tetrazolyl, pyridyl, pyrimidinyl, pyridazinyl and thiadiazinyl radicals and their amino-, alkoxy-carbonyl- (less than 3 carbon atoms), alkyl- (less than 3 carbon atoms), phenyl-, hydroxyl-, nitro-, halogen-, carboxyl-, thiomethyl-, thioand thiol-substituted derivatives.

According to the present invention, the amount of the thiol compound added to the alkali metal thiocyanate or ammonium thiocyanate is preferably 0.8% by weight at the maximum. Addition of more than 0.8% of the thiol compound leaves much undissolved, and since addition of 0.8% or less is effective, the use of more than 0.8%

These compounds are dissolved in water, lower aliphatic alcohol such as methanol, ethanol, isopropanol, and the like, acetone, dioxane and the like, and used in the form of a solution.

By using the treating solution of the present invention, it is possible to utilize the good properties of an alkali metal thiocyanate or ammonium thiocyanate as stabilizer and to get rid of the unfavourable effects thereof. The thiol compound used in the present invention is generally poor in solubility so that its sole use as stabilizer does not produce a solution having a concentration suflicient enough to be a treating solution. In the present invention, the thiol compound is not used as stabilizing agent, but as an addition agent in a small amount, so that a poorly soluble thiol compound can be employed without the least inconvenience. The thiol compound even in the form of a super-saturated solution is inadequate by itself to function as a stabilizer, since the photosensitive material treated therewith is printed-out and then fades at high temperature and in high humidity. Nevertheless, the joint use of an alkaline metal thiocyanate or ammonium thiocyanate and a small amount of a thiol compound achieves good effects such as prevention of change in tone. Due to this fact, the present invention has accomplished improvements in the stabilization using an alkali metal thiocyanate or ammonium thiocyanate.

The abovementioned thiol compounds may be used together with salts of heavy metals such as Ni, Co, Cd, Zn and Au, which can form soluble or insoluble complex salts with the stabilizing agent to stabilize the image. The treating solution of the present invention may contain a hardening agent, carboxymethyl cellulose or alcohol.

The thiol compound according to the present invention can also be used in the form of a separate solution, without incorporating it into the stabilizing solution. For instance, the developed photosensitive material is treated with a stablizing agent such as ammonium thiocyanate and then immersed in a solution containing at least 0.01% and up to about 0.8% based on the weight of the silver complex forming agent, by weight of the thiol compound when compared on the basis of the same volume. This aqueous solution may contain a fluorescent brightening agent. The time of immersion is about 2 seconds but it is not so limited.

In order to facilitate the understanding of this invention, examples will be given hereafter. It should be understood that this invention is not limited by such examples but by the appended claims.

EXAMPLE 1 An emulsion was prepared by adding 20 grams of hydroquinone to one kilogram of a gelatino silver chloride emulsion (silver chloride 4.3% by weight) and adjusting the pH to 5.0. This emulsion was coated on a paper support.

The coating was exposed, developed in an activator solution having the following composition:

Grams Sodium hydroxide 30 Sodium sulfite (anhydrous) 40 Potassium bromide 5 Water to make 1 liter.

and immediately thereafter subjected to the stabilizing treatment using a solution having the following composition:

ammonium thiocyanate175 grams borax2 grams 6 potassium metabisulfite-130 grams Formalin (20% )l50 cm. 0.4% alcoholic solution of 2-mercaptoimidazole100 cm. Water to make 1000 cm.

The procedure for preparing the solution was as follows: potassium metabisulfite was dissolved in 300 cc. of water and then Formalin was added. The solution after mixing was heated by the heat of reaction. After the temperature of the solution was lowered to room temperature, 0.4% alcohol solution of Z-mercaptoimidazole was added, then water was added until the total amount of the solution was attained to 1000 cm.

The image stabilized with this solution showed sufficient stability after drying. Even when preserved under a severe condition of high humidity such as RH the decrease in density of image was less than that of an image treated with a solution which contained the agents listed above excepting Z-mercaptoimidazole. That is, the preservation property was better.

The result of a test carried out under a condition of 100% RH at a room temperature is as follows:

Decrease in density after 4 hours Stabilizing solution without Z-me'rcaptoimidazole 0.61 Stabilizing solution containing Z-merca-ptomidazole 0.31

EXAMPLE 2 A photosensitive paper of silver chloride was treated with a stabilizing solution having the following composition in the same way as in Example 1.

ammonium thiocyanate175 g.

borax2 g.

potassium metabisulfiate g.

Formalin (20% )l50 cm.

0.6% alcoholic solution of 2-mercaptobenzimidazole water to make 1000 cm.

The result of the test is as follows:

Decrease in density after 4 hours Stabilizing solution without 2-mercaptobenzimidazole 0.61 Stabilizing solution containing Z-mercaptobenzothiazole 0.33

The print was exposed to the light of a fluorescent lamp of 1,000 lux for 24 hours immediately after drying. Con tamination of white parts was apparently less than the case when a stabilizing solution without Z-mercaptobenzimidazole was employed.

EXAMPLE 3 A photosensitive paper of silver chloride was treated with a stabilizing solution having the following composition in the same way as in Example 1.

ammonium thiocyanate-175 g.

borax2 g.

potassium metabisulfite130 g.

Formalin (20% cm.

NiCl 5 g.

0.6% alcoholic solution of 2-mercaptobenzimidazole water to make 1000 cm.

The result of test is as follows:

Decrease in density after 4 hours Stabilizing solution without Z-mercaptobenzimidazole 0.45 Stabilizing solution containing 2-mercaptobenzimidazole 0.18

EXAMPLE 4 A photosensitive paper of silver chloride was treated The result of the test was as follows:

Decrease in density after 4 hours Stabilizing solution without -ethoxycarbonyl-2-mercapto-4-methylthiazole 0.56 Stabilizing solution containing S-ethoxycarbonyl-Z- mereapto-4-methylthiazole 0.35

EXAMPLE 5 A photosensitive paper of silver chloride was treated with a solution having the following composition in the same way as in Example 1.

ammonium thiocyanate175 g.

borax2 g.

potassium metabisulfite-BO g.

0.7% alcoholic solution of 2-mercaptobenzothiazole water to make 1000 cm.

The result of the test was as follows:

Decrease in density after 4 hours Stabilizing solution without 2-1nercaptobenzothiazole 0.61 Stabilizing solution containing Z-mercaptobenzothiazole 0.37

EXAMPLE 6 A film coated with the emulsion of silver chloride bromide (silver bromide 10%) which contains gelatine and hydroquinone, was exposed, developed and then treated with a stabilizing solution having the following composition in the same way as in Example 1.

ammonium thiocyanate-175 g.

borax-2 g.

potassium metabisulfite130 g.

0.l% alcoholic solution of 2-mercaptobenzoxaZole-l0O water to make 1000 cm.

The result of the test was as follows:

Decrease in density after 4 hours Stabilizing solution without 2 mercaptobenzoxazole 0.53 Stabilizing solution containing Z-mercaptobenzoxazole 0.29

EXAMPLE 7 A photosenstive paper of silver chloride was. treated with a stabilizing solution having the following composition in the same way as in Example 1.

ammonium thiocyanate-175 g.

borax2 g.

potassium metabisulfite120 g.

0.4% alcohol solution of 2 mercapto 5 methyl 1,3,4-

oxadiazole-ZOO cm.

CoSO -0.1 g.

water to make 1000 cm.

The result of the test was as follows:

Decrease in density after 4 hours Stabilizing solution without 2-mercapto-5-methyl- 8 1,3,4-oxadiazole 0.65 Stabilizing solution containing 2-rnercapto-5-methyl- 1,3,4-oxadiazole 0.40

EXAMPLE 8 A photosensitive paper of silver chloride was treated with a solution having the following composition in the same way as in Example 1.

ammonium thiocyanate-l75 g.

borax2 g.

potassium metabisulfite1 20 g.

0.7% alcoholic solution of S-mercapto-l-phenyl-lH-tetrazole200 cm.

water to make 1000 cm? The result of the test was as follows:

Decrease in density after 4 hours Stabilizing solution without. S-mercapto-l-phenyllH-tetrazole 0.59 Stabilizing solution containing S-mercapto-l-phenyllH-tetrazole 0.33

EXAMPLE 9 A photosensti've paper of silver chloride was treated with a solution having the following composition in the same way as in Example 1.

ammonium thiocyanatel65 g.

borax-2 g.

potassium metabisulfite g.

0.2% alcoholic solution of 4-hydroxy-2-mercapto-6-methylpyrimidinel50 cm.

water to make 1000 cm.

The result of the test was as follows:

Decrease in density after 4 hours Stabilizing solution without 4-hydroXy-2-mercapto- 6-methylpyrimidine 0.57 Stabilizing solution containing 4-hydroxy-2-mercapto-6-methylpyrimidine 0.39

EXAMPLE 10 A photosensitive paper prepared by coating the emulsion of silver chlorobromide (silver bromide 10%) containing gelatine and hydroquinone, was exposed, developed and then treated with stabilizing solution having the following composition in the same way as in Example 1.

ammonium thiocyanateg.

borax--2 g.

potassium metabisulfitel20 g.

0.6% alcoholic solution of 2-mercapto-4-phenyl-1,3,4-

thiadiazoline-S-thione-15 0 cm.

water to make 1000 cm.

The result of the test was as follows:

Decrease in density after 4 hours Stabilizing solution without 2-mercapto-4-phenyl- 1,3,4-thiadiazoline-5-thione 0.57 Stabilizing solution containing Z-mercapto-Lphenyl- 1,3,4thiadiaZoline-S-thione 0.38

EXAMPLE 11 A photosenstive paper of silver chloride was treated with the following solution in the same way as in Example 1.

ammonium thiocyanateg, borax2 g.

potassium metabisulfitel30 g. formalin (20% )150 em. water to make 1000 cm.

The treated paper Was then immersed in a 0.1% aqueous solution of potassium salt of 2-mercapto-4-phenyl- 1,3,4-thiadiazoline-5-thione for 2 seconds.

The result of the test was as follows:

EXAMPLE 12 A photosensitive paper of silver chloride was treated with a stabilizing solution having the following composition in the same way as in Example 1.

borax2 g.

ammonium thiocyanate250 g.

sodium bisulfite70 g.

0.5% alcoholic solution of 2-amino-5-mercapto-1,3,4-

thiadiazole-l cm.

water to make 1000 cm.

The result of the test was as follows:

Decrease in density after 4 hours Stabilizing solution without Z-amino-S-mercapto- 1,3,4-thiadiazole 0.61 Stabilizing solution containing 2amino-5-mercapto- 1,3,4-thiadiazole 0.20

EXAMPLE 13 Z-mercaptoxazole was used in place of 2-mercaptoimidazole in Example 1. The same result was obtained.

EXAMPLE l4 4-mercaptopyridine was used in place of 4-hydroxy-2- mercapto-6-methylpyrimidine in Example 9. A similar result was obtained.

EXAMPLE 15 3-mercaptopyridazine was used in place of 4-hydroxy- Z-mercapto-6-methylpyrimidine in Example 9'. A similar result was obtained.

EXAMPLE l6 2-mercapto-4-methyl-1,3,4-thiadiazine was used in place of 2-amino-5-mercapto-1,3,4-thiadiazine in Example 12. A similar result was obtained.

EXAMPLE 17 A photosensitive paper of silver chloride was treated with a solution of the following composition in the same way as in Example 1.

Ammonium thiocyanate175 g. Borax2 g.

Potassium metabisulfite120 g. ZnCl 1O g.

Water to make 1000 cm.

The photosensitive material thus treated in which the unexposed silver chloride was converted to the stabilized silver complex salt was then dipped for about 2 seconds in a solution having the following composition and dried.

7-dimethylamino-4-methylcumarin (fluorosecent brightening agent)8 g.

0.7% methanol solution of 5-mercapto-1-phenyltetrazolel00 cc.

Water to make 1000 cc.

When tested as in Example 10, a similar result was obtained.

EXAMPLE 18 The efiect of our invention is further illustrated by 10 the following comparison of the following three stabilizing solutions: (1) a stabilizing solution containing ammoniurn thiocyanate alone (Recipe 3), (2) a stabilizing solution containing ammonium thiocyanate and a thiol compound (Recipes 1 and 2) and (3) a stabilizing solution containing a thiol compound alone (Recipes 4 and 5).

A photographic silver chloride emulsion layer containing hydroquinone was exposed, developed in an activator solution containing 5% NaOH and 0.01% KBr, and then subjected to the stabilizing treatment with the following stabilizing solutions:

Recipe 1 Borax2 g. Ammonium thiocyanate-250 g. Sodium bisulfite70 g. 0.5% alcoholic solution of Z-mercaptobenzimidazole- 50 cm. Water to make 1000 cm. pH 4.5

Recipe 2 Borax2 g. Ammonium thiocyanate250 g. Sodium bisulfite-70 g. 0.8% alcoholic solution of Z-amino-S-mercapto-1,3,4-

thiadiazole-50 cm.

Water to make 1000 cm. pH 4.5

Recipe 3 Borax2 g. Ammonium thiocyanate--250 g. Sodium bisulfite70 g. Water to make 1000 cm? pH 4.5

Recipe 4 Disodium orthophosphate15 g. Monosodium orthophosphate10 g. Glacial acetic acid12 cm. 0.8% alcoholic solution of 2-amino-4-mercapto-l,3,4-

thiadiazo1e90 cm. Water to make 1000 cm. pH 4.6

Recipe 5 Sodium carbonate53 g.

0.8% alcoholic solution of 2-amino-5-mercapto-1,3,4-

thiadiazole150 cm.

Water to make 1000 cm.

The photosensitive paper thus treated was placed under the following conditions:

Ileft as it was.

'II-placed for a day under the condition of 100% RH at 35 C.

III-placed for 4 hours under the condition of RH at 50 C.

The resulting color of the image is shown in the following table.

Recipe 1 2 3 4 5 Condition:

I A A A(B) C 1 D 1 II C B E C III B B E 1 Print-out. NOTE .A=Alm0st unchanged, black; B =Slightly brownish; C =da1'k brown; D =Brown; E Yellowish brown.

1 1 the prints stabilized with the acidic treating solution (Recipe 4) were greater than those of the prints stabilized with the alkaline treating solution (Recipe 5).

When a small amount of a thiol compound is added to the solution containing ammonium thiocyanate (Recipes 1 and 2), the change of image color was so little that the stabilized image could be preserved for a long time under normal conditions.

We claim:

1. A process for the production of photographic stable visible images in a silver halide photographic emulsion layer containing latent images, which comprises developing said latent images in an alkaline solution and stabilizing said layer by applying an aqueous solution containing a silver complex-forming agent and between 0.01% and 0.8%, based on the weight of said silver complex forming agent, of a thiol compound, said silver complex-forming agent being a member selected from the group consisting of an alkali metal thiocyanate and ammonium thiocyanate and said thiol compound being a member selected from the group consisting of Z-mercaptoimidazole, Z-rnercaptobenzimidazole, S-ethoxycarbonyl-mercapto-4-methyl thiazole, Z-mercaptobenzothiazole,

Z-mercaptoxazole,

Z-mercaptobenzoxazole, 2-amino-5-mercapto-1,3,4-thiadiazole, 2-mercapto-4-phenyl-1,3,4-thiadiazoline-S-thione, 2-mercapto-5-methy1- 1,3 ,4-oxadiazole, S-mercapto-l-phenyll H-tetrazole, 4-mercaptopyridine, 4-hydroxy-2-mercapto-6-methy1-pyrirnidine,

12 3-mercaptopyridazine, and 2-mercapto-4-methyl-1,3,4-thiadiazine.

2. A stabilizing solution containing a silver complexforming agent and between 0.01% and 0.8%, based on the weight of said silver complex-forming agent, of a thiol compound, said silver complex-forming agent being a member selected from the group consisting of an alkali metal thiocyanate and ammonium thiocyanate and said thiol compound being a member selected from the group consisting of Z-mercaptoimidazole, Z-mercaptobenzimidazole, S-ethoxycarbonyl-mercapto-4-methyl-thiazole, 2-mercapt0benzothiazole,

Z-mercaptoxazole,

2mercaptobenz0xazole,

Z-amino-S -mercapt0-1 ,3 ,4-thiadiazole, 2-mercapto-4-phenyl-1,3,4-thiadiazoline-5-thione, 2-mercapto-5-methyl-l ,3,4-oxadiazoie, imercaptol-phenyl- 1 H-tetrazole, 4-mercaptopyridine, 4-hydroXy-2-mercapto-6-methyl-pyrimidine, S-mercaptopyridiazine, and 2-mercapto-4-methyl-1,3,4-thiadiazine.

References Cited UNITED STATES PATENTS 1/1962 Tregillus et al. 96-29 6/1964 Smith et al 9661 

